The blower motor on a Dodge is a single speed and the speed is reduced by passing current through the resistor. The spring like resistance wire gets hot, turning some of the energy into head and dropping the voltage. With the lower voltage, the motor spins slower. So if the motor runs full tilt but not otherwise, that's a sign the resistance wire is broken or the connection inside the switch is bad. If the motor only runs at the slower speed, then either the contacts inside the fan switch are cruddy and need to be cleaned, the switching mechanism inside the swtich is busted or the bearings are dragging on the motor. The squirrel cage fan should spin easily and continue to spin for a few seconds after you give it a good twrill. If the bearings are dragging, most older small, direct current motors can be disassembled and the bronze bushings greased. If you can't get the motor apart because it's pressed together, you can sometimes get enough lubricant into the fan end by adding a drip aaround the shaft with the motor in the vertical position, spin it, add more and so on. On the opposite end, you can drill a small hole in the center of the protrusion where the end of the shaft is and add a few drips of motor oil. Grease is the perfered lubricant, but WD40 is ok for getting things loosened up and then using a heavy grade motor oil.
I can't remember if the fan motor can be disassembled or not. As for telling a single speed motor apart from those that actually have high and low speed windings, the single speed will have 2 wires, a ground and a hot wire. True multi speed motors will have 3 wires on a 2 speed and 4 on a 3 speed. These days, nearly all 3 or more speed motors use a rheostat and single speed motor. To test the fan motor itself on a Dodge, all you have to do is disconnect the + wire plastic connector at the firewall and run a jumper wire from the positive battery terminal to it. The motor should run full tilt. If it doesn't run, then the motor is probably shot and if it runs slowly, then the bearings are probably dragging and need lubing.
